Basic Fern Identification

For some time I had been wanting to learn more about ferns, so I took advantage of a workshop on fern identification being held at the Wahkeena Nature Preserve in Fairfield County, Ohio. Wahkeena is a great place to learn about ferns since 29 species of fern grow there (Wahkeena’s official blog publishes a list of their local fern species). Naturalist Tom Shisler led the workshop which is called Focus on Ferns. In this post I’m going to introduce you to a number of common ferns found in Ohio by summarizing Tom’s presentation.

Cinnamon fern (Osmundastrum cinnamomeum); it’s always a pleasure to encounter a large ground cover of ferns like these while hiking. The above photo was taken in while hiking in the Oak Openings Metro Park in the Toledo area.

Fern Terminology

Prior to taking the workshop at Wahkeena I had photographed a number of beautiful ferns thinking that I would be able to identify them later via the photo. However after taking the workshop I came to the conclusion that I’m not going to be able to identify many of these because I didn’t gather enough data in my photographs. When attempting to identify a fern, its important to look closely at one of the fronds, to turn it over and look at its underside for reproductive structures, and also to examine the frond’s stalk making note of its color and texture. I’m going to make observations about a species key characteristics as I describe the ferns below, but to make the descriptions easier to follow, I’ll start by introducing a few technical terms.

Tom Shisler introduced us to some basic terms while we explored the trails, frequently stopping to point out the distinguishing characteristics of different fern species.

The frond of a fern consists of a stalk with a green, leaf-like growth emerging from it. Usually the leaf-like material of a frond is sub-divided into multiple leaf-like growths. When the blade is divided in this way, each division is called a pinna (pronounced “PIN-nuh”; the plural is pinnae, pronounced “PIN-knee”). Some pinnae are further divided into pinnules. In some cases the pinnules are further divided into lobes. The more that the leaf-like material is divided, the more feathery or lacy the frond looks. Fronds that are divided again and again are said to be finely-cut.

This is the underside of a frond showing the big pinna (plural, pinnae), the smaller pinnule, and the reproductive structure known as the sorus (plural, sori).

Unlike flowering plants, ferns reproduce via spores instead of seeds. An individual spore is so tiny that it is invisible to the naked eye. However the spores are housed in visible structures while they are developing. These structures are known as sori (pronounced “SORE-eye”; the singular is sorus, pronounced “SORE-us”). The sori grow on the underside of a frond. Observing the location and appearance of these sori is a big help in identifying the fern’s species. In some species each individual sorus is easily seen (check out the photo above), but in other species the presence of sori just seems to change the color, texture and shape of the frond.

Some ferns species produce mostly sterile fronds (without sori), while also producing one or more fertile fronds (with sori). Other ferns consist entirely of fertile fronds. And in some fern species, the sori only emerge from some of the pinnae, while they are absent from the rest of the pinnae.

Examining the stalk of a frond can also be a help in identifying the fern species. The part of the stalk from the ground to the beginning of the frond’s leafy area is known as the stipe. The portion of the stalk to which the leafy material is attached is known as the rachis. Noting the stalk’s color and its texture (for instance, whether the stalk is hairy), can be helpful in identifying the fern species.

Identifying Fern Species

In the headers below, the common name links to an article at Wikipedia about that species. A list of all the species also appears at the end of this article with information about that species distribution in Ohio.

Christmas fern is common in Ohio. Looking closely at the frond, you’ll see that there is a “bump” on the top of each pinna near the stalk. A mnemonic for remembering that this is Christmas fern is to imagine that each pinna is a sled, and that the bump is Santa sitting in the sled.

Pinna of Christmas Fern (Polystichum acrostichoides); imagine that the bump on the top of the pinna is Santa sitting in his sled.

Here’s a look at the whole fern.

Christmas Fern (Polystichum acrostichoides)

The spores only develop on the top portion of the frond. The fertile pinnae curl up as the spores on them develop. The sori underneath the pinnae are not seen distinctly, but they make the entire underside turn brown.

To identify a Maidenhair fern, take a good look at the stalk. The stipe (the leafless, bottom portion of the stalk) is long and black. At the top of the stipe, the stalk divides into two rachises (the part of the stalk with leafy material). The two rachises are mirror images of one another. Each rachis bends in a semi-circle with the distant end of the rachis drawing near the end of the other rachis. The overall effect is as though you are looking down on a raised, horizontal circle of fronds.

Lady Fern is recognized by its reddish or wine-colored stalk. In addition its pinnea tend to be widely spaced on its rachis (top portion of the stalk).

Lady Fern (Athyrium filix-femina); note the reddish stalk.

Lady Fern (Athyrium filix-femina); note the reddish stalk.

Lady Fern (Athyrium filix-femina); in this frond the stalk is more reddish toward the bottom. This closer view also helps to illustrate how widely spaced the pinnae are, particularly toward the bottom.

These two fern species are closely related and resemble each another. The easiest way to distinguish between them is to note the difference in the location of the reproductive sori. In the Cinnamon Fern all the sori are located on a dedicated fertile frond that looks very different from the remaining fronds. The fertile frond shoots up vertically from the center of the fern, and it is the color of cinnamon which gives this species its common name. The top-most photo in this post is that of a forest floor covered in Cinnamon ferns. Below is a closer look of one of the plants.

Cinnamon fern (Osmundastrum cinnamomeum)

And here’s a closer look at the fertile frond of a Cinnamon fern.

Fertile frond of the Cinnamon fern (Osmundastrum cinnamomeum)

The pinnae of the Cinnamon fern and the Interrupted fern are similar in shape and in their arrangement. Below is a closer look at the underside of a Cinnamon fern frond.

Cinnamon fern (Osmundastrum cinnamomeum) viewed from beneath

Note that there are no sori on the underside of the pinnae since the sori are all located on the fern’s cinnamon-colored fertile frond. So the above frond is a sterile frond.

Below is the very similar-looking sterile pinnae of an Interrupted fern, but this time viewed from the top.

Sterile pinnae of the Interrupted fern (Osmunda claytoniana)

The most characteristic feature of the Interrupted fern is the location of the sori on the frond. Unlike the Cinnamon fern, the sori are not located on a distinct fertile frond. Like the Christmas fern the Interrupted fern has fertile pinnae (with sori) and sterile pinnae (without sori) on the same frond. In the Christmas fern all the fertile pinnae are located at the top of the frond and all the sterile pinnae are at the bottom. In contrast an Interrupted fern has sterile pinnae both at the top and bottom. But in the middle the frond the sterile pinnae are interrupted by a few brown, droopy-looking fertile pinnae as shown below.

Silvery spleenwort is also known as Silvery glade fern because it grows in openings or glades. The foliage, though green, is a bit yellowish. The sorai are arranged on the back of the pinnae in a herringbone pattern. Each sorai is elongated, looking like a hot dog bun, or a spleen. It is said to be “silvery” because the length of the stem is covered in white hairs.

Silvery spleenwort viewed from underneath. It has little white hairs emerging from the rachis (stem).

Silvery spleenwort (Deparia acrostichoides) viewed from the top.

A variety of fern species are referred to as spleenworts, a name that was inspired by their sori. Instead of being circular in shape, each sorus is shaped like a “spleen”. For all practical purposes, you could say that it is also shaped like a hot dog bun. As to the name, wort, this is an old-fashioned word for “plant.”

I was unable to locate pinnae with sori, so I am including a public domain illustration showing the sori on the underside of the pinna.

This is a small fern with long, narrow fronds. Each plant typically has three fronds. The stem is “ebony” or black near the bottom, but it may be green near the top. The sori are spleen-shaped (or you can think of each of them as having the same shape as a hot dog bun) just like the Silvery spleenwort that we saw earlier.

Ebony spleenwort (Asplenium platyneuron) – Tom indicated that this species was typically found with three fronds. If you look at the rachis (stem) near the bottom, you’ll see that it is black which is how it gets the common name, Ebony.

Ebony spleenwort (Asplenium platyneuron) – this is a closeup of the pinnae near the top of the frond. The ebony (or black-colored) stem is near the bottom.

At the fern’s base, the sterile fronds are triangular in shape and nearly horizontal. All the sori are located on an erect, fertile frond shooting up from the fern’s center. When the fertile frond is mature, you can tap it and see it emit a cloud of spores.

Fertile and sterile fronds of the Virginia Grape Fern(Botrychium virginianum); also known as the Rattlesnake Fern.

Before the fertile frond is mature, it is green and the pinnae have a beaded, grape-like appearance. Or you might look at the rounded, tightly grouped fertile pinnae and be reminded of the end of a rattlesnake’s tale. So its the fertile frond that gives rise to its two common names, Grape fern and Rattlesnake fern.

Immature fertile frond of the Virginia Grape Fern(Botrychium virginianum); also known as the Rattlesnake Fern. The immagure fertile frond is green.

Mature fertile frond of the Virginia Grape Fern(Botrychium virginianum); also known as the Rattlesnake Fern. The mature fertile frond can be anywhere from brown to a light tan color.

The sterile pinnae of the Virginia Grape Fern are finely cut and have a lacy appearance.

The Sensitive fern and the Broad Beech fern are similar in that the both have a winged rachis (stem-like structure to which the pinnae are attached); the wing is a leafy edging found along the sides of this stem. The photo below illustrates what I mean.

A winged rachis (stem) is one in which leafy material runs along the length of the rachis.

The fern in the above photo is a Sensitive fern. Below is a photo of the entire frond.

Sensitive fern (Onoclea sensibilis)

And the photo below shows a patch of Sensitive ferns. Intermixed with the green, sterile fronds are brown, fertile fronds.

Sensitive fern (Onoclea sensibilis) — you can see some dark, fertile fronds mixed in with this group.

Below is a closeup look at the top of a Broad beech fern. You can see that it also has a winged rachis. However the pinnae are grouped much closer together than those of the Sensitive fern. In addition, the margin or edge of the pinna of a Sensitive fern has more a of wavy look, while the pinna of a Broad beech fern has almost rectangular looking pinnules.

Pinnae of Broad beech fern (Phegopteris hexagonoptera)

Below you can see what the entire Broad beech fern looks like.

Broad beech fern (Phegopteris hexagonoptera)

Lifting up one of the fronds, you can see that this species of fern has a brown stipe (the stem from ground to leaf). This is another of its distinguishing characteristics.

I didn’t see a Royal fern during this visit to Wahkeena, but it is listed as one of the species that grows there. Each pinna is attached to the the stem at a single point. The margins (edges) of the pinnae are smooth.

Royal fern (Osmunda regalis) – note the dark, bluish-green fertile fronds in the center. When more mature, the fertile frond will be brown.

I wouldn’t have even recognized that this was a fern if left to my own devices. The frond is completely undivided, so it looks like a single leaf emerging from the ground. This leaf is the sterile frond of the fern known as Adder’s tongue. To reproduce the plant puts forth a distinct fertile frond next to the sterile one (not shown in the following photo).

In the photo below, the fern’s fronds are floating on the water next to the lily pad. Each frond looks like a four-leaf clover. Prior to this workshop, I didn’t even know that there were aquatic ferns!

Water clover (Marsilea)

Information on Ferns at Wahkeena

One more session of the workshop, Focus on Ferns, is being held this year at Wahkeena on July 13, 2104 at 1:00 P.M. For information on this and other programs for the amateur naturalist, check out Wahkeena’s scheduled programs. In addition, the official blog for the Wahkeena Nature Preserve has a page dedicated to ferns here.

As a help identifying ferns in the field, Wahkeena’s naturalists recommended the book, Fern Finder by Hallowell & Hallowell. It used to be offered for sale in Wahkeena’s Nature Center. However the book is going out-of-print, so they no longer stock it. It is still available at Amazon, and we were able to obtain a copy from there. If you are interested in shopping for it at Amazon, here’s the link: Fern Finder: A Guide to Native Ferns of Central and Northeastern United States and Eastern Canada (Nature Study Guides). The small size of the book makes it a good one to take along while hiking.

The book, “Fern Finder”

Additional reading

The fern species below are arranged alphabetically according to their common names. The scientific name links to a Wikipedia article where you can learn more about the species. Following that is a link to a USDA map showing that specific species’ distribution in Ohio.

This was a really helpful post! I’ve been on guided walks during which naturalists have identified ferns and talked a bit about them, but my eyes have tended to glaze and I’ve forgotten everything nearly immediately! This information was laid out clearly, and I know I’ll refer to it again.
One fascinating fern you don’t mention (maybe it’s not at Wahkeena – I think it requires limestone) is the walking fern. Are you familiar with it? It’s very “un-ferny.”

Thanks for your kind words about this post! I have seen photos of the Walking fern, but so far haven’t laid eyes on it myself. It’s listed as one of the fern species that are present at Wahkeena, so I hope to be able to see it in the future. I’m thinking that I can add it to this post later. I absolutely agree about it looking very “un-ferny”.

Hiking Blogs

Welcome New Visitors!

The TrekOhio Guide lists parks and nature preserves in Ohio. Navigate to a county listing via our menus above, or go there directly by typing its name after trekohio.com/, for example, http://trekohio.com/hocking.

The TrekOhio Blog is where Bob and Deb Platt publish articles on both parks and nature topics. To see an alphabetical listing of the parks that we've reviewed so far, select Reviews from the menu above.